1. Field of the Invention
This invention is related to the general field of sewing machines and accessories to improve their versatility. In particular, the invention provides a new set of accessories designed specifically to enable the sewing of narrow strips and corners of thick, or hard to penetrate, material that cannot otherwise be sewn with standard equipment.
2. Description of the Related Art
The general workings of a sewing machine are the same whether designed for thin fabric, such as in clothing, or for thick material, such as in leather or multilayer applications. The material is fed forward while being held with the layers to be sewn facing toward the inside and through the stitching mechanism of the machine. The upper portion of the sewing mechanism includes a stroking vertical needle, threaded with an upper thread, that moves up and down through a horizontal needle plate. The material to be sewn is fed over the needle plate and automatically moved forward between stitches by a toothed feeding mechanism that works either within or in cooperation with the plate. During each stitching cycle, a pressure foot clamps the layers of material being sewn on the needle plate while the downward motion of the threaded needle pierces through the material to start the stitch. Upon reaching the other side of the needle plate, the upper thread is engaged by a lower thread carried by a shuttle hook in a rotating shuttle in the lower portion of the sewing mechanism. The needle then reverses its motion and carries the lower thread, engaged by the upper thread, through the stitch hole in its upward travel. As the needle releases the material in its upward travel, the pressure foot also releases its clamp on the material, which thus remains free to be shifted forward by the feeding mechanism. The cycle then begins anew as the pressure foot moves down to clamp the material and the needle goes through it in its new position (that is, one stitch forward from the old one).
Another kind of machine functions essentially the same way, except that the material is fed through by the forward displacement of the needle while it moves upwards at the end of each stitch. The material is kept in place by the pressure foot while the needle travels downward to engage the lower thread; the pressure foot is then lifted slightly as the needle travels upward and forward, thus displacing the material to a new stitch position; and finally the pressure foot again clamps the material against the needle plate as the needle is released from the material and shifts backward to initiate a new stitch cycle. U.S. Pat. No. 4,991,526 to Jean Blanc (1991) describes such a sewing machine incorporating a modified needle plate insert and a pressure foot for improved stitching of thick material. The invention comprises a needle-receiving slot that provides a side guide for avoiding needle deflections and loss of stitches otherwise caused by the needle penetration into thick layers of material.
Some machines feature two pressure feet, instead of only one. The first one is a plate pressure foot that serves the same general purpose of the single pressure foot in other machines; that is, it clamps the material to the needle plate while the needle is forming the stitch and it releases the material while it is being advanced between stitches. The second one is a needle pressure foot that serves as an additional clamp to the material during the penetration of the needle and as a feeding mechanism, in conjunction with the needle, to move the material forward between stitches. The needle pressure foot is typically smaller and contained within the toes of the larger plate pressure foot. The needle pressure foot and the needle remain parallel at all times and shift their horizontal position together moving forward as the plate pressure foot is released during the needle's upward stroke, and then they shift back together, free of the material, to start a new stitch during the needle's downward stroke after the plate pressure foot has again pinned the material to the needle plate. To my knowledge, prior art pressure feet are generally symmetrical and consist of two toes, one on the inside and the other on the outside of the vertical needle, that press on the material being sewn. In the case of double pressure-foot machines, the two toes of the needle pressure foot are usually connected at the tip, defining a hole or slot at the center of the foot through which the needle travels during the stitching operation.
One of the problems common to all kinds of machines is the difficulty encountered while trying to sew along narrow seams and corners, especially when the material is thick or also hard to penetrate, such as leather in saddle making. The present invention is an improvement of the double pressure-foot type of machine, directed at providing modified pressure feet and other accessory parts that make it possible to sew narrower seams in both thin and thick material and to place stitches in corners or other difficult-to-reach spots than is currently possible with standard equipment.